Rolling mill having a controlled hydraulic prestress range and other gap adjusting means for initial operation and for adjustment to said range



P 1969 J. DOWSING ETAL 3,454,245

ROLLING MILL HAVING A CONTROLLED HYDRAULIC PRESTRESS RANGE AND OTHER GAP ADJUSTING MEANS FOR INITIAL OPERATION AND FOR ADJUSTMENT TO SAID RANGE Filed May 2. 1966 3 Sheets-Sheet 1 u 5 n n m I- A n m h 1 V rm m m w i 6 W m a m f 7 m N m M 3 W J mm a u "w v 7 u 6 rm %9 g i 7 I O I? AL 8 |||l|I|.l|L W 0 8 7 9 J J 2 6 w L 9 Fl lllllllllllllllll L m l m 9 /w n A H Sept. 2, 1969 J. nowsme ETAL 3,

ROLLING MILL HAVING A CONTROLLED HYDRAULIC PRES'IRESS RANGE AND OTHER GAP ADJUSTING MEANS FOR INITIAL OPERATION AND FOR ADJUSTMENT T0 sAID RANGE Filed May 2, 1966 3 Sheets-Sheet 2 Fla. 2.

Sept. 2, 1969 Filed May 2, 1966 J. DOWSING ETAL ROLLING MILL HAVING A CONTROLLED HYDRAULIC PRESTRESS RANGE AND OTHER GAP ADJUSTING MEANS FOR INITIAL OPERATION AND FOR ADJUSTMENT TO SAID RANGE 3 Sheets-Sheet 5 RAISE LOWER GA TE UN/ T SET SET UP GA TE WIDTH HOUSING LOAD IND/CA TOR HOUSING LOAD IND/CATOR (NEAR S/DE) (DR/VE SIDE) United States Patent 3,464,245 ROLLING MILL HAVING A CONTROLLED HYDRAULIC PRESTRESS RANGE AND OTHER GAP ADJUSTING MEANS FOR INI- TIAL OPERATION AND FOR ADJUSTMENT TO SAID RANGE John Dowsing and Peter Richard Ashworth Briggs,

Sheffield, and Clifford Sturdy, Chesterfield, England, assignors to Davy and United Engineering A Company Limited, Shefi'ield, England, a British company Filed May 2, 1966, Ser. No. 581,399 Claims priority, application Great Britain, May 3, 1965, 18,586/65 (Filed under Rule 47(a) and- 35 U.S.C. 116) Int. Cl. B21b 37/02, 31/20, 31/16 US. Cl. 72-16 22 Claims ABSTRACT OF THE DISCLOSURE The invention is concerned with the automatic control of a prestressed rolling mill, in which a hydraulically produced prestressing force is applied to certain of the stand components and there are adjusting means independent of the hydraulic prestressing force for adjusting the roll gap setting. In the invention, uniform strip thickness is maintained by automatically controlling the prestressing force. If the prestressing force goes outside a given range, the roll gap adjusting means are operated to return the prestressing force to within range. Initially, the prestressing force is kept constant and control exerted by adjustment of the roll gap adjusting means; thereafter, automatic control is transferred to the prestressing force.

This invention relates to rolling mills and in particular to prestressed rolling mill stands. In this specification, a prestressed rolling mill stand (referred to hereinafter as of the type described) is to be understood as comprising two roll assemblies, each having a work roll and optionally a back-up roll, hydraulically operated prestressing means, which apply a prestressing force or forces to at least some of the stand components which elastically deform under the rolling load and which, when so deformed, cause a change in the roll gap, and adjusting means independent of the prestressing means for adjusting the roll gap setting. By roll gap setting is meant in this context the gap between the working surfaces of the work rolls, assuming zero rolling load and zero prestressing force or forces. Under the action of the rolling load and/ or the prestressing force or forces fiective when the prestressing force or forces depart from the roll gap setting may be monitored for all rolling loads and prestressing forces, regardless of the actual roll gap.

One form of prestressed mill of the type described has the roll assemblies mounted in a housing and the prestressing means acting between the roll assemblies tending to force those assemblies apart; the adjusting means then act to limit the movement apart of the assemblies. Other forms of prestressed mill stand are however applicable to the present invention, such as that having adjustable spacers between the assemblies and the prestressing means between the housing and one assembly, and the similar construction in which spacers be tween the assemblies are replaced by spacer bars acting between the top or bottom of the housing and the Patented Sept. 2, 1969 "ice arise however where the variation in the pressure of the liquid supplied to the prestressing means becomes excessive and no further change in the force or forces applied by the prestressing means is possible. In these circumstances, uniformity of thickness of the rolled material may be lost until changes in the characteristics of the material entering the stand enable the pressure to return to a safe value, with the outgoing material at the required thickness.

In the present invention, there are provided means, elfective when the presetting force or forces depart from a given range, for actuating automatically the adjusting means until the force or forces is or are restored to within the given range. Thus, the prestressing means operate to control material thickness while the prestressing force can be retained in the safe range; when it goes out of range, the adjusting means are actuated to restore the force or forces to within the range. In the result, loss of uniformity of thickness is kept to a minimum.

The invention will be more readily understood by way of example from the following description of a rolling mill stand and its control system, reference being made to the accompanying drawings in which FIGURES 1, 2 and 3 diagrammatically show the stand and the control system and are intended to read together.

The rolling mill stand is represented on the drawing by one of the two housings 12, it being understood that the other housing is identical. Housing 12 has a housing window 13 in which are located an upper backup roll chock 14 for the upper back-up roll 15 and the lower back-up roll chock 16 for the lower back-up roll 17. Chock 16 rests on a thrust pad 18 at the bottom of the window 13, while a screw 20 threaded in the top of the housing engages the upper surface of chock 14 with a load cell 21 interposed.

Nested in recesses 22 in the chocks 14, 16 are work roll chocks 23, 24 for upper work roll 25 and lower work roll 26, respectively. Four rams, of which two are shown at 27, 28 act between back-up roll chocks 14, 16 of each housing and serve as both balance cylinders and prestressing cylinders as will be explained hereinafter. Ram 28 acts through a load cell 30 in the chock 14. Rams 31 between the chocks 23, 24 act as work roll balance cylinders, while rams 32 between chock 14 and chock 23 and rams 33 between chock 16 and chock 24 act to control the bow of the work rolls 25, 26 for shape control.

The screw 20 is driven by a screwdown motor 35 controlled by raise and lower contactors 36. The screw 20 is coupled to a synchro 37 connected through line 38 to a screw position indicator (not shown). A second synchro 40 also coupled to screw 20 is connected through a differential synchro 41 coupled to the screw of the other housing and through a second differential synchro 42 to a synchro receiver 43, the rotor of which is geared to a motor 44 and the slider of a potentiometer 46. The output winding of synchro 43 is connected through a switch 47 to the input of an amplifier 48, the output of which controls the motor 44. Motor 44 has a coupled tacho generator 50, the output from which is fed back to amplifier 48. The rotor of synchro 43 is also geared to a clutch 5 1 which, when engaged, couples synchro 43 with the rotor of differential synchro 42. In operation, a displacement of either synchro 40 or synchro 41 causes a misalignment signal from synchro 43 to appear at the input of amplifier 48, causing motor 44 to drive the rotor of synchro 43 until the misalignment signal becomes zero. As slider 45 is driven by the rotor of synchro 43, the signal from potentiometer 46 on line 52 represents the mean position of screw 20 and the corresponding screw of the other housing.

The rams 27, 28, 31, 32 and 33 are supplied with oil under pressure by a pump 60 and a connected accumulator 61, the oil being supplied on line 62 at a constant pressure. Thus the work roll balance cylinders 31 are connected to line 62 through a valve 63, which sets the pressure of the oil delivered to rams 31, and through a cock 64, by which rams 31 may be either connected to valve 63, isolated from valve 63 or vented. Line 65 also connected to the output side of cock 64 leads to the work roll balance cylinders of the other housing, while a pressure relief valve 66 protects rams 31 from over-pressure.

Rams 32, '33 are connected to line 62 similarly, i.e., through a pressure adjusting valve 63A and a cock 64A; line 65A leads to the similar rams on the other housing. Valve 63A is adjustable to control the camber of the work rolls for shape control.

The four rams 27, 28 which prestress the housing 12 and chocks 14, 16 are supplied from line 62 through a cock 70 similar to cock 64 and two servo-operated valves, one of which is shown at 71, and by which the pressure in the rams is adjusted. Line 72 connected to the output side of cock 70 leads to the rams in the other housing, corresponding to rams 27, 28, there being servooperated valves similar to valve 71 and controlled in parallel with it.

As before mentioned, the force supplied by the prestressing rams 27, 28 is measured by the load cell 30, the electric signal from which is applied to one winding of a transformer 73; a second input winding of transformer 73 is fed from the corresponding load cell in the other housing. It is of course preferable to have a separate load cell 30 for each of the four prestressing rams and to sum the outputs, but on grounds of economy a single cell for each housing is used. The output winding of the transformer thus emits a signal on line 74 representing the prestressing force (P) and this signal is applied through a differencing circuit 75 to one pole of switch 76. The differencing circuit 75 is also supplied with a signal from a device 77 representing the required operating pressure for rams 27, 28, the signal applied to switch 76 then representing the departure of the prestressing force from the desired value. Switch 76 is connected to the input of an amplifier 78 controlling the servo-operated valve 71. The signal on line 74 is also applied through line 80 to an input of a summing amplifier 81; this amplifier has a number of inputs, one of which is line 52 carrying the screw position signal.

Thirdly, the signal on line 74 is applied to a differencing circuit 82, which is also supplied with a signal from a device 83 representing the nominal prestressing load. The difference signal is applied through switch 84 to a gate unit 85 controlled by a manually operated device 86. If the sign-a1 from diiferencing circuit 82 is greater than the gate width set by device 86 a signal is applied by gate unit 85 to operate appropriately the contactors 36 for the screwdown motor 35.

Load cell 21 produces on line 87 a signal representing the load to which load cell 21 is subjected. This signal is applied to one winding of a transformer 88, while a similar signal from the load cell of the other housing is applied on line 90 to a second input winding. The signal on the output winding of transformer 88, representing the total load, is applied on line 91 as a further input to amplifier 81. A further output from load cell 21 is applied on line 92 to an indicator 93. The load on the other housing is shown on a similar indicator 93A supplied on line 92A. The signals on lines 92, 92A are combined, modified for nonlinearity of the deflection/ rolling load characteristic, as described in US. Patent No. 3,128,630 to P. R. A. Briggs, issued Apr. 14, 1964, and applied on line 94, as a further input to amplifier 81 as a compensation for such nonlinearity. A still further input to amplifier 81 is supplied on line 95 from a manually operated device signal generator 96 which is set So is the roll gap setting of the work rolls, when the mill is subjected to no force; this'is represented by the setting of screws 20 and is indicated by the signal on line 52 is the effective elastic deformation of the housings 12 and back-up roll chocks 14, 16 where F is the load to which load cell 21 is subjected and which is represented by the signal on line 91, and Mh and Mc are the coefiicients of elasticity respectively of the housings 12 and of the back-up roll chocks is the roll flattening, where Fr is the rolling load and Mr is the coefficient of elasticity of the rolls, the effect of rams 31, 32 being ignored. The gauge error is thus where h' is the required gauge as set on device 96. Since F=Fr+P, this can be written:

where P is the prestressing force, as measured by load cells 30 and represented by the signal on line 80. The summing amplifier 81, which has as inputs the values S0, F, P and h, solves this equation, so that the output from amplifier 81 on line 97 represents the gauge error.

The gauge error signal is applied to a servo 98 driving a pointer 99 to indicate the gauge error, and through a normally closed switch 111 and line 100 to the second pole of switch 76. The gauge error signal is also applied on line 101 to the second poles of switches 47 and 84. Lastly, the gauge error signal is applied to a diflerencing circuit 102 to which is also applied the gauge error signal from either a contact type gauge detector 103 or a noncontact type gauge detector 104, the signal on line 105 representing the gauge error, as before. If, through long term drift in the system, the gauge error from amplifier 81 deviates from the gauge error on line 105, there is an output on line 105 from the circuit 102. Line 105 is connected through switch 106 to an integrator 107 which is of the type comprising a motor driving a potentiometer and a tacho-generator the output of which is fed back in opposition to the input of the motor. Thus, if there is a disparity between the gauge error signals on lines 97 and 101, a gradually increasing signal is applied through a switch 108 to a further input of amplifier 81 to reduce the disparity to zero. It will be appreciated that, in the short term, the gauge detectors 103, 104 have no effect, gauge error being detected by changes in screw setting and the response of load cells 21, 30 and it is only in the long term that the detectors 103 or '104 alfect the gauge error signal.

The control of the rolling mill to produce instant gauge strip falls into two parts, the setting-up period and the running period. In the former, when rolling is started, the prestress force applied by the rams 27, 28 is kept constant and the screws 20 are automatically controlled until they are positioned for the required gauge. Thereafter, in the latter period, the screws 20 are kept in their set position, and the pressure in rams 27, 28, and thus the prestress force is continuously controlled to maintain constant gauge strip. If, however, during the latter period, the pressure in rams 27, 28, and thus the prestressing force, should depart from the datum value set on device 83 by a preset amount set by the device 86, the screws 21 are again operated to return the pressure to midrange.

During the setting up period, switches 76 and 84 are changed over from the positions shown. The servooperated valves 71 are then controlled by the difference signal from the differencing circuit 75 and the pressure in rams 27, 28 is maintained strictly at the value set on 5 device 77; if the pressure should depart from that value, the difference signal appears at the input of amplifier 78 to appropriately modify the pressure until the difference signal is returned to zero. At the same time, the gauge error signal at the output of amplifier 81 is applied on line 101 and through switch 84 to gate unit 85. If the gauge error departs from zero by a value exceeding the gate width set on device 86, the gate unit passes the gauge error signal to operate the contactors 36, thereby driving the screws 20, until the gauge error signal falls again within the gate width.

When the mill is running on gauge, as indicated by the meter 99, the switches 76, 84 are changed over, either automatically or manually, to the positions shown. The gauge error signal on line 97 is now applied through line 100 and switch 76 to amplifier 78, to control the servooperated valves 71. In this run period, therefore, the screws 20 are kept stationary and, if any gauge error should occur, resulting in a signal on line 97, the pressure in rams 27, 28 is altered until the gauge error signal is returned to Zero. This control operation being effected hydraulically is quicker in operation than the control of the screws 20, which entails the delays inhereint in the operation of the contactors 36 and in the inertia of the motors 35 and screws 20. As a result, smoother control is elfected and more uniform gauge strip is achieved.

If, during the run period, the pressure in the rams 27, 28 should depart from the nominal value, set by device 83, a signal is applied through switch 84 to the gate unit 85. If the departure should exceed the gate width as set on 86, the signal is passed by the gate unit 85 and operates the contactors 36, thus causing the screws 20 to be moved until the signal from diflferencing circuit 82 is again less than the gate width. In this way, the pressure in the rams 27, 28 is kept within a safe Working range, without loss of gauge.

The zero of potentiometer 46 is set initially by changing over switch 47 from the position shown and, with no work in the mill, operating the screws 20 until the work rolls 25, 26 just touch one another; the screwdown contactors 36 may be controlled manually on line 110. In addition, clutch 51 is engaged. In this position of the rolls, the gauge error signal should be Zero. If, because of incorrect setting of potentiometer 46, there is a signal on line 101, that signal causes motor 44 to drive potentiometer 45 until the gauge error signal is zero. At the same time, the rotor of difierential synchro 42 is driven through clutch 51, so that on changing over switch 47 again and disengaging clutch 51, no mismatch signal is emitted by synchro 43.

After one or more coils have been rolled, the monitor integrator 107 will have built up an input signal which, passing through switch 108, causes adjustment of the signal from amplifier 81 for on-gauge rolling. To avoid depending on the long term stability of the monitor integrator 107, this signal is incorporated in the initial setting for the next coil by effecting the zeroising operation described in the preceding paragraph, but with the setting device 96 set for the gauge or strip just produced, switches 106, 108, 111 are opened; switch 108 removes the signal from amplifier 81 and this resulting error sig nal from amplifier 81, being applied through line 101 to amplifier 48, reset the potentiometer 46 for zero gauge error signal. The opening of switch 106 simultaneously causes the signal from integrator 107 to reduce rapidly to zero ready for the moment of reconnection preparatory to the rolling of the next coil.

We claim:

1. In a rolling mill stand comprising two roll assemblies between which the material to be rolled is passed; means for restraining separation of said assemblies; hydraulically operated prestressing means to apply a prestressing force to at least some of the stand components which elastically deform under the rolling load and which, when so deformed, causes a change in the roll gap; and adjusting means independent of the prestressing means for adjusting the roll gap setting; a gauge control system comprising:

means for controlling automatically said prestressing force to maintain the thickness of said material substantially at a datum value; and means, operated when said force departs from a given range, for actuating automatically said adjusting means until said force is restored to within said range. 2. In a rolling mill stand comprising two roll assemblies between which the material to be rolled is passed; means for restraining separation of said assemblies, hydraulically operated prestressing means to apply a prestressing force to at least some of the stand components which elastically deform under the rolling load and which, when so deformed, cause a change in the roll gap; and adjusting means independent of the prestressing means for adjusting the roll gap setting; a gauge control system comprising:

means for generating a control signal dependent on the departure from a datum value of the thickness of said material leaving the stand; means for controlling said prestressing means by said control signal to maintain said departure substantially zero; normally inoperative means for actuating said roll gap adjusting means; and means responsive to the value of said prestressing force and operative when said force departs from a given range to render said actuating means effective to cause operation of said adjusting means in a direction to return said force to within said range. 3. A prestressed rolling mill stand according to claim 2 in which the means for generating the control signal comprise means for generating a first signal in accordance with the roll gap setting, means for generating a second signal or signals in accordance with the change in the roll gap from the roll gap setting due to the rolling load and the prestressing force or forces, datum signal means for generating a signal in accordance with the datum value, and means for combining the signals together to form the control signal.

4. A prestressed rolling mill stand according to claim 3 in which the prestressing means are located between the roll assemblies, tending to force the assemblies apart, the adjusting means act to resist separating movement of the assemblies, and the means for generating the second signal comprise a first force-transducer for detecting the prestressing force or forces, and a second forcetransducer for detecting the force to which the adjusting means are subjected, the signals from the transducers being combined in the combining means.

5. A prestressed rolling mill stand according to claim 4 in which each roll assembly comprises a back-up roll, back-up roll chocks, and work roll chocks carried by the back-up roll chocks and the prestressing means comprise hydraulic rams disposed between the back-up roll chocks of the two assemblies.

6. A prestressing rolling mill stand according to claim 4 in which the adjusting means are mechanical and are disposed between a stand housing and one of the roll assemblies, and the means for generating the first signal is a position transducer operatively coupled to the adjusting means.

7. A prestressed rolling mill stand according to claim 2 in which the means for rendering eifective the adjusting means comprises means for generating a datum force signal in accordance with the mid-value of the given range, means for comparing the datum force signal with a signal representing the force or mean force applied by the prestressing means and giving a force error signal, and a gate to which the force error signal is applied and which causes actuation of adjusting means when the force error signal exceeds a given value.

8. A prestressed rolling mill stand according to claim 2 including means for controlling the adjusting means by the control signal, and means for rendering ineffective the means controlling the prestressing means for rendering effective the means controlling the adjusting means by the control signal.

9. A prestressed rolling mill stand according to claim 8 in which there are means for maintaining substantially constant the force or mean force applied by the prestressing means, while the controlling means for the prestressing means are ineflfective.

10. In a rolling mill stand comprising two roll assemblies between which the material to be rolled is passed;

means for restraining separation of said assemblies;

hydraulically operated prestressing means to apply a prestressing force to at least some of the stand components which elastically deform under the rolling load and which, when so deformed, cause a change in the roll gap; and

adjusting means independent of the prestressing means for adjusting the roll gap setting;

a gauge control system comprising:

means for maintaining said prestressing force at a predetermined value;

means for generating a control signal dependent on the departure from a datum value, of the thickness of said material leaving the stand;

means for actuating said roll gap adjusting means;

means for controlling said actuating means by said control signal to maintain said departure substantially zero;

means for alternatively controlling said prestressing means by said control signal to maintain said departure substantially at Zero;

and means for rendering ineifective said maintaining means and controlling means for the actuating means, and for rendering etfective said controlling for said prestressing means.

11. A gauge control system according to claim 10 in which said means for rendering effective and ineffective comprise switch means for applying to said controlling means for said prestressing means alternatively said control signal and a signal representing the departure of said prestressing force from said predetermined value, and controlling the application of said control signal to said controlling means for said actuating means.

12. In a rolling mill stand comprising two roll assemblies between which the material to be rolled is passed; means for restraining separation of said assemblies;

hydraulically operated prestressing means to apply a prestressing force to at least some of the stand components which elastically deform under the rolling load and which, when so deformed, cause a change in the roll gap; and

adjusting means independent of the prestressing means for adjusting the roll gap setting;

a gauge control system comprising:

means for producing a first signal dependent on said roll gap setting;

means for producing a second signal dependent on said prestressing force;

means for producing a third signal which varies with the rolling load applied by said material being rolled to said roll assemblies;

means for generating a datum thickness signal;

means for combining together said first, second, third and datum signals to produce a control signal representing the departure of the thickness of said material leaving the stand from the datum thickness; and

means operated by said control signal for controlling said adjusting means to maintain said control signal substantially zero.

13. A prestressing rolling mill stand according to claim 12 in which the prestressing means act between the two roll assemblies and act to force'those assemblies apart, While the adjusting means are mechanical and resist the force or forces applied by the prestressing means.

- 14. A prestressed rolling mill stand according to claim 13 in which the first signal producing means is a position transducer coupled to the adjusting means.

15. Aprestressed rolling mill stand according to claim 13 in which the second signal producing means comprise a first force-transducer responsive to the prestressing force or forces, and the third signal producing means comprise a second force-transducer ,responsive to the force applied to the adjusting means by the prestressing force and the rolling load.

16. A prestressed rolling mill stand according to claim 15 in which said means for restraining separation of said assembly comprises two housings receiving the respective roll ends, the prestressing means are hydraulic rams acting between the roll assemblies at each housing, and the first force transducer measures the force applied by at least one ram of each housing.

17. A prestressed rolling mill stand according to claim 16 in which each roll assembly comprises a back-up roll, backup roll chocks slidably arranged within the housings, and work roll chocks for a work roll carried by the backup roll chocks, the hydraulic rams acting between the back-up roll chocks of the two housings.

18. A prestressed rolling mill stand according to claim 16 in which the adjusting means are mechanical and act between the housings and one of the roll assemblies.

19. A prestressed rolling mill stand according to claim 18 in which the adjusting means are screws carried in the housings and acting on one of the roll assemblies and the first signal producing means in a position transducer operatively coupled to at least one of the screw and giving a signal dependent on the angular position of said at least one screw.

20. A prestressed rolling mill stand according to claim 18 in which the second force-transducer is interposed between the adjusting means and one of said housing and said roll assembly.

21. A prestressed rolling mill stand according to claim 12 in which there are means for maintaining substantially constant the prestressing force applied by the prestressing means.

22. Aprestressed rolling mill stand according to claim 21 in which force maintaining means comprise means responsive to the prestressed force or forces applied, means for comparing the force or the mean force with a datum value, and means for adjusting the pressure of the liquid supplied to the prestressing means, in accordance with difference.

References Cited UNITED STATES PATENTS 2,903,926 9/1959 Reichl 72-8 3,247,697 4/1966 Cozzo 72-240 3,285,049 11/1966 Neumann 72-246 3,315,507 4/1967 Marten 72-16 3,327,508 6/1967 Brown 72-6 3,208,251 9/1965 Hulls et al. 72-16 3,228,219 1/1966 Fox 72-16 FOREIGN PATENTS 955,164 4/1964 Great Britain.

MILTON S. MERHR, Primary Examiner U.S. Cl. X.R. 72-240, 246, 248 

